Process for producing mixed esters from aldehydes

ABSTRACT

The Tischenko reaction is employed to produce mixed esters from acetaldehyde and isobutyraldehyde with maximum production of ethyl acetate, isobutyl acetate, and isobutyl isobutyrate, and minimum product of undesirable products such as ethyl isobutyrate. Isolation of essentially pure preferred ester products is achieved through a novel continuous distillation system. A holding tank maintained at an elevated temperature with respect to a Tischenko reactor is employed to increase the yield of preferred ester products. Distillation streams containing undesirable impurities and ethyl isobutyrate are cycled to a condensation catalyst reactor for use as catalyst solvent, and to effect conversion of ethyl isobutyrate to preferred ester products.

United States Patent 1 Wright, Jr. et al.

[ 1 Jan. 30, 1973 [54] PROCESS FOR PRODUCING MIXED ESTERS FROM ALDEHYDES[75] Inventors: Howard N. Wright, Jr.; Hugh J. Hagemeyer, Jr., both ofLongview,

Tex.

[73] Assignee: Eastman Kodak Company,

Rochester, NY.

[22] Filed: Aug. 7, 1970 [21] Appl. No.: 61,896

[52] US. Cl ..260/494, 252/429 A, 260/491,

260/499, 260/615 A, 260/638 C, 260/643 R [51] Int. Cl. ..C07c 67/00,C07c 67/06 [58] Field of Search ..260/494, 499

[56] References Cited UNITED STATES PATENTS 3,081,344 3/1963 Hagemeyer,Jr. et al ..260/494 3,398,166 8/1968 Duke et al. ..260/494 PrimaryExaminer-Vivian Garner Att0meyCecil D. Quillen, Jr. and Daniel B. Reece,Ill

[57] ABSTRACT The Tischenko reaction is employed to produce mixed estersfrom acetaldehyde and isobutyraldehyde with maximum production of ethylacetate, isobutyl acetate, and isobutyl isobutyrate, and minimum productof undesirable products such as ethyl isobutyrate. Isolation ofessentially pure preferred ester products is achieved through a novelcontinuous distillation system. A holding tank maintained at an elevatedtemperature with respect to a Tischenko reactor is employed to increasethe yield of preferred ester products. Distillation streams containingundesirable impurities and ethyl isobutyrate are cycled to acondensation catalyst reactor for use as catalyst solvent, and to effectconversion of ethyl isobutyrate to preferred ester products.

8 Claims, 2 Drawing Figures PATENTEDJMI 30 I973 SHEET 10F 2 mQQjm .5

om mi HOWARD N WRIGHT ,JR HUGH J. HAGEMEYER,JR.

Wk 1' ENZORs ATTORNEY PATENTEll-Mllfifl ms 3.714.236

sum 2 or 2 Y Ethyl |sobqy1g1e l x I l 4O 60 MOLE PERCENT ACETALDEHYDE INFEED g 1. E 1 5 x i v Lo 2 1 l l 1 \i 8 8 8 9 8 .LOflOOUd NI 831.931N3083d 310W HOWARD u WRIGHT,JR. HUGH J. HAGEMEYER,JR JNVENTORS M1). 4mbzwi ATTORNEY PROCESS FOR PRODUCING MIXED ESTERS FROM ALDEHYDES Thisinvention relates to the synthesis and recovery of mixed esters frommixed aldehydes by means of the Tischenko reaction. More particularly,the invention relates to a process for the preparation of mixed estersfrom acetaldehyde and iso-butyraldehyde and recovery of essentially pureethyl acetate, isobutyl acetate and isobutyl isobutyrate.

The condensation of aldehydes by the well known Tischenko reaction,which may be written:

ZRCHO RCOOCH R wherein R is an alkyl group and the catalyst is a metalalkoxide condensation catalyst such as aluminum alkoxide, has been usedextensively to produce certain lower esters on an industrial scale. Forexample, ethyl acetate has been produced fora number of years by theprocess of reacting acetaldehyde in the presence of an aluminum ethoxideslurry.

One industrial process for reacting dissimilar aldehydes to produceesters comprises oxidizing an aldehyde to acid in one production unit,hydrogenating an aldehyde to alcohol in another production unit, andesterifying the resulting alcohol and acid in a third production unit.Such a three-step process has the disadvantage of requiring an excessiveamount of expensive equipment. The use of the Tischenko reaction toproduce mixed esters from dissimilar aldehydes has been reported, buthas not heretofore been used on an industrial scale due to thedifficulty in separating the ester products. Attempts to employ theTischenko reaction to produce ester products from the reaction ofacetaldehyde and isobutyraldehyde has heretofore resulted in a mixedester product containing undesirable azeotropes and considerable amountsof ethyl isobutyrate. As is well known, ethyl isobutyrate has only verylimited industrial importance due to its objectionable odor and whenseparated in a conventional distillation system tends to remain as acontaminant in the preferred ester products.

According to the present invention, a continuous process for thepreparation and recovery of essentially pure esters from a Tischenkoreaction of acetaldehyde and isobutyraldehyde free of alcohol azeotropesand ethyl isobutyrate contamination is disclosed. The process comprisesintroducing into a reaction zone essentially dry, acid-free reactantscomprising a mixture of acetaldehyde and isobutyraldehyde, andcondensing the reactants at a condensation temperature in the presenceof a metal alkoxide condensation catalyst for a time sufficient toconvert at least 90 percent of the reactants to a reaction productmixture comprising ethyl acetate, isobutyl acetate, isobutylisobutyrate, and ethyl isobutyrate. The reaction product mixture andunconverted reactants are then passed from the reaction zone to aholding zone maintained at an elevated temperature. During residence inthe holding zone, unconverted aldehydes are preferentially converted tothe preferred ester products.

The resulting reaction product mixture then passes from the holding zoneto a first distillation zone of the novel distillation system of thepresent invention. An overhead distillate stream is withdrawn from thefirst distillation zone and is fed into a second distillation zone. Anoverhead distillation stream and a bottom residual stream are withdrawnfromthe second distillation zone, the bottom residual stream passing toa third distillation zone. Essentially pure ethyl acetate is withdrawnfrom the third distillation zone as an overhead product stream while abottom residual stream is withdrawn from the third distillation zone andpassed to a fourth distillation zone. An overhead distillate stream anda bottom residual stream are withdrawn from the fourth distillationzone, the overhead distillate stream passing to a fifth distillationzone and the bottom residual stream returning to the first distillationzone. A side product stream consisting essentially of isobutyl acetateis withdrawn from the fifth distillation zone. Also withdrawn from thefifth distillation zone are an overhead distillate stream and a bottomresidual stream, the bottom residual stream returning to the firstdistillation zone.

The bottom residual stream of the first distillation zone is passed to asixth distillation zone, from which sixth distillation zone is withdrawna catalyst sludge stream and an overhead distillate stream which ispassed to a seventh distillation zone. A side product stream consistingessentially of isobutyl isobutyrate and an overhead distillate streamare withdrawn from the seventh distillation zone, the overheaddistillate stream returning to the first distillation zone.

The overhead distillate streams of the second, fifth and seventhdistillation zones are recycled to a metal alkoxide condensationcatalyst formation zone. Ethyl isobutyrate is preferentially convertedin the catalyst formation zone to the preferred ester products which canbe recovered in the novel distillation system of the present invention.

The novel process of the present invention will be described in moredetail by reference to the drawings wherein:

FIG. 1 is a schematic flow diagram of a preferred embodiment of theprocess; and

FIG. is a graph showing the product distribution obtained according tothis invention.

Referring to FIG. 1, a catalyst solution comprising condensing amountsof a metal alkoxide condensation catalyst is supplied from a catalystreaction zone or tank 28 via line 32 into circulating line 11 of reactorzone 8. A reactant mixture of essentially dry, acid-free acetaldehydeand isobutyraldehyde is simultaneously fed to the reaction zone 8 viafeed line 10. Aluminum alkoxide is the preferred condensation catalystemployed in the process and a metal chloride promoter such as aluminumtrichloride is normally also used. The molar ratio of the aluminumalkoxide to the metal chloride promoter such as, for example, aluminumtrichloride, is between about 4:1 to about 14:1 with the preferred ratiobeing about 4.5:1 to about 7:1. The solvent for the catalyst is theoverhead taken from distillation columns 2 and 5. This is highlydesirable since it permits the use of all by-products of the reactionand ultimately results in the by-products being converted to salableesters. Normally, the solvent will contain from about 10 to about 20percent, and preferably 15 percent, of the overhead from column 2 withthe remainder being the overhead from column 5. The catalyst mixture issoluble in the Tischenko reactor product.

The reactant mixture passes along feed line 10 to the reaction zone 8via circulating line 11. By maintaining the temperature of reaction zone8 at from about to about C., allowing a reactant residence time of fromabout 3 to about 6 hours, and adjusting the aluminum alkoxide catalystfeed rate to from about 0.1 to about 5.0 percent by weight of the totalfeed, a conversion of at least 90 percent of the reactants is effectedto yield a reaction product mixture comprising ethyl acetate, isobutylacetate, isobutyl isobutyrate, and ethyl isobutyrate. The reactoroverflow comprising the reaction product mixture and unconvertedreactants is passed via line 13 to a circulating hold tank 9 maintainedat a temperature of between about 20 C. to about 40 C., preferably about30C., and of such a size as to provide a residence time sufficient tocomplete preferential condensation of the unconverted reactants to thedesired mixed ester products. The overflow from holding tank 9 passes tostripper column 1 via line 14.

The residence time necessary for the unconverted reactants to bepreferentially condensed may vary somewhat dependent upon thetemperature, catalyst concentration, etc., but normally will fall withinthe range of about 5 to about 30 hours. If the condensation of theunconverted reactants is not substantially completed prior to its beingfed into stripper column 1 an excess amount of aldehydes will be fedinto the distillation system. In the first two columns these excessaldehydes will react with isobutanol and ethanol to form acetals whichbreak down in later columns to form water, low boilers which boil below70 C. at atmospheric pressure and other undesirable products. Thepresence of the undesirable products in turn results in the base heatersof the columns 1 and 6 being plugged and the whole system, includingproducts, being contaminated with decomposition products.

The effectiveness of the holding tank 9 in preventing the entry ofunconverted reactants into column 1 is clearly illustrated in Table 1wherein the percent (by weight of the total feed) of unreacted aldehydesfed into the holding tank via line 13 is compared to the weight percentaldehydes discharged from the tank through line 14. The hold time of thetank is 16 hours at approximately 30 C.

' TABLEI Weight Percent (by weight of total feed) Unreacted Aldehydes inReactor Overflow (line 13) Hold Tank Discharge (line 14) The strippercolumn 1 overhead distillate stream comprising ethyl acetate, ethylisobutyrate, isobutyl acetate and other low boiling fractions passes vialine 15 to distillation column 2. The overhead distillate stream fromcolumn 2 comprising aldehydes, ethanol, and small quantities of ethylacetate is withdrawn via line 16, and advantageously passed via line 22to catalyst reactor 28. The bottom residual stream from column 2 is fedvia line 17 to distillation column 3. The overhead product stream ofcolumn 3 comprising essentially pure ethyl acetate is drawn off via line18 and collected as a product while the bottom residual stream fromcolumn 3 passes via line 19 to distillation column 4. The overheaddistillate stream from column 4 passes via line 20 to distillationcolumn 5 while the bottom residual stream is recycled to column 1 vialines 21 and 23. The overhead distillate stream of column 5 is drawn offvia line 22 and, advantageously, this stream may be returned to thecatalyst reactor 28. The side product stream from column 5 consistingessentially of pure isobutyl acetate is drawn off via line 33 andcollected as a product.

The bottom residual stream from column 1 passes via line 24 todistillation column 6. The overhead distillate stream from column 6 ispassed via line 25 to distillation column 7 while the bottom streamcomprising spent catalyst sludge is drawn off via line 26. The overheaddistillate stream from column 7 comprising isobutanol and other lowboiling components is drawn off via line 27 and returned to the catalystreactor 28 The side product stream from column 7 consisting ofessentially pure isobutyl isobutyrate is drawn off via line 30 andcollected as a product.

Table 11 illustrates the temperature and pressure ranges under which thecolumns are operated.

TABLE 11 Temperature at Top of Column Column Maximum Minimum PreferredPressure 1 117 C. 78 C. Approximately atmospheric 2 78 C. 60 C. 72 C.Atmospheric to psig 3 77 C. 77 C. 77 C. Approximately atmospheric 4 117C. 108 C. 1 13 C. Approximately atmospheric 5 1 17 C. 108 C. 1 14 C.Approximately atmospheric 6 150 C. 145 C. 147 C. 50 mm Mercury toatmospheric 7 147 C. 108 C. C. 100 mm Mercury to atmospheric Statedtemperatures are for operation at atmospheric pressure. Depends upondesired ratio of products being produced.

The following examples illustrate more fully the processes of thepresent invention whereby mixed esters are produced fromisobutyraldehyde and acetaldehyde with a minimum production of ethylisobutyrate, and recovered as essentially pure ester products free ofethyl isobutyrate and azeotropic contamination. In the examples,numerals designating process equipment such as reactors, distillationcolumns, etc., are those of FIG. 1.

EXAMPLE 1 One-thousand sixty pounds per day of dry acetaldehyde, 1,380pounds per day of dry isobutyraldehyde and a catalyst solutioncontaining 6.0 moles of aluminum alkoxide per mole of anhydrous aluminumchloride sufficient to provide 0.20 percent aluminum based on totalfeed, are added to a 100 gallon capacity Tischenko reactor 8. Reactortemperature is maintained at 5 C. and reactor residence time is 4 hours.Aluminum alkoxide feed rate to the Tischenko reactor 8 isadjusted tomaintain less than 5 percent unreacted aldehydes in the reactoroverflow. Overflow from the Tischenko reactor 8 is introduced into acirculating 1000 gallon capacity hold tank 9, the level of which ismaintained at about 500 gallons to provide a 24 hours residence time.The temperature of the material in the hold tank is kept at about 30 C.

The hold tank 9 overflow, which consists of a reaction product mixturecomprising 0.2 percent acetaldehyde, 0.3 percent isobutyraldehyde, 23.9percent ethyl acetate, 7.1 percent ethyl isobutyrate, 48.4 percentisobutyl acetate, 18.0 percent isobutyl isobutyrate, 0.2 percent acetalsand 1.9 percent catalyst and glycol esters, is introduced from the holdtank via line 14 to stripper column 1. Column 1 is operated atatmospheric pressure to separate isobutyl acetate and lower boilingcomponents overhead. Temperatures along the column average 1 12 C. atthe top, 120 C. at the mid dle, 145 C. at the bottom and 152 C. in thebase heater. Reflux ratio is maintained at a value greater than 4 to 1.

Stripper column 1 overhead distillate stream is fed into aldehydedistillation column 2 via line 15. Column 2 is operated at atmosphericpressure to separate aldehyde, ethyl alcohol and some ethyl acetateoverhead. Temperatures along column 2 average 71 C. at the top, 83 C. atthe middle, 85 C. at the base, and 111 C. in the base heater. Refluxratio is maintained at a value greater than 20 to 1. Column 2 overheaddistillate stream is drawn off at a rate of 101 pounds per day of lowboilers via line 16. Column 2 residual stream is fed into ethyl acetatedistillation column 3 via line 17. Distillation column 3 is operated atatmospheric pressure to separate pure ethyl acetate overhead.Temperatures along the column average 77 C. at the top, 80 C. at themiddle, and 120 C. in the base heater. Reflux ratio is maintained at thevalue greater than 5 to 1. An overhead distillate product streamcomprising 99.9 percent ethyl acetate is drawn off column 3 via line 18at a rate of 504 pounds per day.

The bottom residual stream of column 3 is fed via line 19 todistillation column 4. This column is operated at atmospheric pressureto separate the lower boiling components from isobutyl isobutyrate.Temperature along the column average 113 C. at the top, 120 C. at themiddle, and 123 C. in the base heater. Reflux ratio is maintained at avalue greater than 3 to 1. The bottom residual stream of column 4 isrecycled to stripper column 1 via lines 21 and 23 at a rate of poundsper hour to insure the absence of isobutyl isobutyrate in distillationcolumn 5. The overhead distillate stream of column 4 is transferred vialine into isobutyl acetate distillation column 5. This column isoperated at atmospheric pressure to separate ethyl acetate, isobutanoland ethyl isobutyrate from isobutyl acetate. Temperatures along thecolumn average 114 C. at the top, 113 C. at the middle, 132 C. at thebase, and 148 C. in the base heater. Reflux ratio is maintained at avalue greater than 5 to 1. Column 5 overhead distillate stream is drawnoff via line 22 at a rate of 560 pounds per day of low boilingcomponents; the take-off rate is adjusted to provide enough isobutylacetate to equal the rate of ethyl isobutyrate in the overhead product.A side product stream consisting of 99.9 percent isobutyl acetate vaporis withdrawn from column 5 via line 33 at a rate of 1186 pounds per day.A bottom residual stream is drawn off column 5 via line 23 and isrecycled to distillation column 1 at a rate of 10 pounds per hour toinsure the absence of acetals in the base of column 5.

The bottom residual stream of column 1 is fed via line 24 into catalyststripper column 6. This column 5 operated at atmospheric pressure toseparate isobutyl isobutyrate from glycol esters and catalyst residue.Temperatures along the column average 147 C. at the top, 150 C. at themiddle, and 250 C. in the base heater. Reflux ratio is maintained at avalue greater than 1 to l. A molten catalyst sludge stream comprisingglycol esters and catalyst residue is removed from the base of column 6via line 26. The overhead distillate stream of column 6 is fed via line25 into isobutyl isobutyrate distillation column 7.

Column 7 is operated at atmospheric pressure to separate isobutanol andother low boiling components from isobutyl isobutyrate. Temperaturesalong the column average 120 C. at the top, 150 C. at the middle, and158 C. in the base heater. An overhead distillate stream is withdrawn ata rate of 10 pounds per hour and returned to catalyst reactor 28 vialines 27 and 22 to insure the absence of isobutanol and low boilers inthe isobutyl isobutyrate product. A side product stream consistingessentially of 99.9 percent isobutyl isobutyl isobutyrate is withdrawnfrom the base of column 7 via line 30 at a rate of 500 pounds per day. Abottom residual stream may be recycled to column 6 at a rate of 10pounds per hour to insure the absence of high boiling components in thebase of column 7.

This example illustrates the operation of the process with 43.5 percentacetaldehyde in the aldehyde feed mixture. A change in the aldehyde feedmixture produces corresponding changes in the quantities removed fromeach distillation column as clearly illustrated in thefollowing-example.

EXAMPLE II Mixed esters are synthesized according to the continuousprocess of Example 1. The Tischenko reactor is operated at 4 to 6 C.with reactor residence time at 3.8 to 4.0 hours, and with sufficientaluminum alkoxide catalyst solution to provide 0.2 percent aluminum,based on total reactor feed. The catalyst solution contains 5.0 moles ofaluminum alkoxide per mole of aluminum chloride. Duplicate runs are madewith 6 aldehyde feed mixtures containing from 20 percent acetaldehydeand 80 percent isobutyraldehyde to 75 percent acetaldehyde and 25percent isobutyraldehyde. Reactor overflow is found to contain 2 to 6percent unreacted aldehyde, which decreases to 0.1 to 0.3 percentunreacted aldehyde after standing 15 hours at 25 C. in a hold tank. FIG.2 graphically illustrates the ester product distribution with respect topercent acetaldehyde in the aldehyde feed mixture, corrected forcatalyst solvent.

FIG. 2 shows an entirely unexpected product distribution. Acetaldehydeis preferentially converted to the acetate group rather than the ethylgroup, while isobutyraldehyde is preferentially converted to theisobutyl group rather than the isobutyrate group. A purely randomproduct distribution would produce a symmetrical isobutyl acetate curvewith a maximum at about 25 percent and the ethyl isobutyrate curve wouldhave been superimposed on the isobutyl acetate curve. Also, the isobutylisobutyrate and ethyl acetate curves would have been mirror images ofeach other.

EXAMPLE in The overhead distillate streams of aldehyde distillationcolumn 2 and isobutyl acetate distillation column 5 of Example I aretransferred via lines 16 and 22 respectively to a catalyst reactor 28.The typical composition of the overhead distillate stream of column 2 isabout 0.2 percent water, 6.6 percent acetaldehyde, 5.9 percentisobutyraldehyde, 0.3 percent low boilers, 1.1 percent ethanol, and 85.9percent ethyl acetate. The composition of the over-head distillatestream of column 5 is 8.3 percent ethyl acetate, 38.9 percent ethylisobutyrate, 3.0 percent and 48.8 percent is butyl acetate.

Jacketed catalyst reactor 28 is charged with 225 pounds of material fromthe previous catalyst reactor batch, 303 pounds of column 2 overheaddistillate, 1680 pounds of column 5 over-head distillate, 240 poundsisobutanol and 50 pounds of aluminum metal turnings. The reactionbetween aluminum and isobutanol is initiated by heating the mixture toabout 70 C. Heat of reaction is removed byvaporizing the solvent esters,condensing the vaporized esters and returning the solvent esters asreflux. Additional cooling needed during the first part of the reactionis provided through the reactor jacket. When the reaction nearscompletion, the reaction mixture is cooled to about 50 C. and 12 poundsof vaporized chlorine is introduced into the bottom of the catalystreactor during a 4 hour period. A reaction mixture is then heated toprovide gentle refluxing for 8 to 12 hours.

Typical aluminum alkoxide catalyst solution contains 0.5 to 1.0 percentunreacted alcohol, 1.57 percent aluminum chloride, 3.77 percent aluminumethoxide, 8.23 percent aluminum isobutoxide, 19.5 percent ethyl acetate,0.6 percent low boilers, 9.8 percent ethyl isobutyrate, 36.6 percentisobutyl acetate and 19.4 percent isobutyl isobutyrate. The conversionof ethyl isobutyrate to other esters is 65.6 mole percent.

Advantageously, the conversion of ethyl isobutyrate to other esters canbe raised to 80 to 90 mole percent when column 5 distillate alone isused as a catalyst solvent. This modification of the process illustratedin FIG. 1 can be accomplished by disconnecting overhead line 16 ofcolumn 2 from theeatalyst reactor 28. If desirable, the catalystsolution from reactor 28 may be passed through a flash column to removelow boiler before it is fed to the reactor. The overhead from column 2is discharged from the process.

EXAMPLE 1v As discussed hereinabove, the hold tank is necessary to theprocess since any unreacted aldehydes entering the distillation reactwith alcohols to produce acetals and water. These acetals in turndecompose on heating to produce alcohols and unsaturated ethers whichare contaminants in the product esters. To illustrate the necessity ofthe hold tank the continuous system of Example is modified to remove thehold tank 9. Thus, the overflow from the Tischenko reactor is introduceddirectly into stripper column 1 The bottom residual stream of column 3is fed into column 5 and the bottom residual stream of column 5 is fedinto column 4 from which is removed an overhead distillate productstream of isobutyl acetate. The Tischenko reactor is operated at 2 C.with 44.5 percent acetaldehyde and 55.4 percent isobutyraldehyde in thealdehyde feed mixture.

The residence time of the reactor is 5 hours and aluminum alkoxidecatalyst concentration is 0.7 percent, based on total weight, asaluminum.

The overflow material from the reactor contains 4.5 percent unreactedaldehydes. The overhead distillate material from column 2 contains 5 to6 percent water and 20 to 25 percent aldehydes. The overhead distillatematerial from column 4 contains 0.3 percent acetals, 5.0 percentisobutanol and unsaturated ethers and 94.7 percent isobutyl acetate. Thebottom residual stream of column 4 contains 0.3 percent unsaturatedethers, 76.1 percent isobutyl acetate and 23.6 percent acetals. Theoverhead distillate of column 6 contains 3.8 percent acetals with theremainder being isobutyl isobutyrate.

EXAMPLE V Mixed esters are synthesized according to the continuousprocess of Example lV except that a hold tank with a capacity of 24hours residence time is added between the Tischenko reactor anddistillation column 1. The Tischenko reactor overflow product contains4.5 percent unreacted aldehyde which is decreased to 1.5 percentaldehyde in the hold tank. The overhead distillate material from column2 contains less than 1 percent water and 12.5 percent aldehydes. Theoverhead distillate material from column 4 contains 95.8 percentisobutyl acetate, 1.4 percent acetals and 2.8 percent isobutanol andunsaturated ethers. The bottom residual stream of column 4 contains 96.0percent isobutyl acetate, 2.6 percent acetals and 1.4 percentunsaturated ether. The overhead distillate of column 6 contained pureisobutyl isobutyrate with only trace amounts of impurities.

The above examples demonstrate that the novel process of the presentinvention avoids the prior art difficulties inherent in the use of themixed Tischenko reaction to produce mixed esters of acetaldehyde andisobutyraldehyde. The present process results in essentially purerecovery of maximum amounts of ethyl acetate, isobutyl acetate, andisobutyl isobutyrate free of azeotropes and ethyl isobutyratecontamination, while unexpectedly concentrating the impurities and ethylisobutyrate in the column 2 and column 5 overhead streams. The processadvantageously employs the undesirable ethyl isobutyrate-rich stream insuch a manner as to assist in condensation catalyst formation whileconverting the undesirable ethyl isobutyrate to other valuable esters.In addition, the use of a holding tank maintained at an elevatedtemperature of from about 20 to 40 C. in a preferred embodiment of thepresent process allows preferential conversion of unreacted aldehydes tothe desired ester products, thereby increasing the yield of the valuableester products.

It will be evident to those skilled in the art that variations in thedistillation columns can be made in the present process, withcorresponding changes in the number of plates in each column, refluxratios, etc. For instance, further examples could be given to show thatcatalyst stripper column 6 of the example can be replaced by a steamdistillation column or an acid wash column. Any such variations,however, must include a drying column, an isobutanol column, and anisobutyl isobutyrate column in the system.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

We claim:

1. A continuous process for the preparation and recovery of essentiallypure esters from acetaldehyde and isobutyraldehyde essentially free ofethyl isobutyrate contaminant which comprises:

1. introducing into a reaction zone essentially dry,

acid-free reactants comprising a mixture of acetaldehyde andisobutyraldehyde, condensing said reactants at a condensationtemperature of about -10 C in the presence of an aluminum alkoxidecondensation catalyst for about 3 to 6 hours to convert at least 90percent of said reactants to a reaction product mixture comprising ethylacetate, isobutyl acetate, isobutyl isobutyrate, and ethyl isobutyratepassing said reaction product mixture and unconverted reactants to aholding zone maintained at a temperature of between about 20 C. to about40 C. for about to 30 hours to substantially complete condensation ofsaid unconverted reactants;

. passing the resulting reaction product mixture of said holding zone toa first distillation zone maintained at about atmospheric pressure witha top temperature of from about 78 C. to about 1 17 C., withdrawingtherefrom an overhead distillate stream comprising aldehydes, ethylisobutyrate, ethyl acetate, isobutyl acetate, isobutanol and low boilingimpurities and a bottom residual stream comprising isobutanol, isobutylisobutyrate, glycol esters and catalyst residue, passing said overheaddistillate stream to a second distillation zone maintained at from aboutatmospheric to about 100 psig pressure with a top temperature of fromabout 60 C. to about 78 C. at atmospheric pressure;

. withdrawing from said second distillation zone an overhead distillatestream comprising aldehydes, ethyl acetate, and low boiling impuritiesand a bottom residual stream comprising ethyl acetate, isobutyl acetateand high boiling impurities, passing said bottom residual stream to athird distillation zone maintained at about atmospheric pressure with atop temperature of about 77 C.;

5. withdrawing from said third distillation zone an overhead distillateproduct stream consisting essentially of ethyl acetate and a bottomresidual stream comprising isobutyl acetate and high boiling impurities,passing said bottom residual stream to a fourth distillation zonemaintained at about atmospheric pressure with a top temperature of fromabout 108 C to about 117C.;

6. withdrawing from said fourth distillation zone an overhead distillatestream comprising isobutyl acetate and low boiling impurities and abottom residual stream comprising isobutyl acetate and high boilingimpurities, passing said overhead distillate stream to a fifthdistillation zone maintained at about atmospheric pressure with a toptemperature of from about 108 C. to about 117 C. and returning saidbottom residual stream to said first distillation zone;

7. withdrawing from said fifth distillation zone an overhead distillatestream comprising isobutyl acetate and low boiling impurities, a sideproduct stream consisting essentially of isobutyl acetate, and a bottomresidual stream comprising isobutyl acetate, acetals and high boilingimpurities; returning said bottom residual stream to said firstdistillation zone;

8. passing said bottom residual stream of said first distillation zoneto a sixth distillation zone maintained at from about 50 mm mercury toabout atmospheric pressure with a top temperature of from about 145 C.to about 150 C. at atmospheric pressure;

. withdrawing from said sixth distillation zone a bottom catalyst sludgestream comprising glycol esters and catalyst residue and an overheaddistillate stream comprising isobutyl isobutyrate and isobutanol,passing said overhead distillate stream to a seventh distillation zonemaintained at from about mm mercury to about atmospheric pressure with atop temperature of about 108 C. to about 147 C. to atmospheric pressure;and

10. withdrawing from said seventh distillation zone an overheaddistillate stream comprising isobutanol and low boiling impurities and aside product stream consisting essentially of isobutyl isobutylisobutyrate.

2. A process according to claim 1 wherein the overhead distillate streamfrom said seventh distillation zone is fed to an aluminum alkoxidecondensation catalyst formation zone wherein an alkanol, halogen andaluminum metal are introduced to form an aluminum alkoxide condensationcatalyst, a solution of aluminum alkoxide condensation catalyst iswithdrawn from said condensation catalyst formation zone and saidsolution of aluminum alkoxide condensation catalyst is passed to saidreaction zone.

3. A process according to claim 1 wherein the overhead distillate streamfrom said fifth distillation zone is fed to an aluminum alkoxidecondensation catalyst formation zone wherein an alkanol, halogen andaluminum metal are introduced to form an aluminum alkoxide condensationcatalyst, a solution of aluminum alkoxide condensation catalyst iswithdrawn from said condensation catalyst formation zone and saidsolution of aluminum alkoxide condensation catalyst is passed to saidreaction zone.

4. A process according to claim 3 wherein said aluminum alkoxidecondensation catalyst formation zone is maintained at a temperature ofbetween about 110 C. and about C.

5. A process according to claim 1 wherein the overhead distillate streamfrom said second distillation zone is fed to an aluminum alkoxidecondensation catalyst formation zone wherein an alkanol, halogen andaluminum metal are introduced to form an aluminum alkoxide condensationcatalyst, a solution of aluminum alkoxide condensation catalyst iswithdrawn from said condensation catalyst formation zone and saidsolution of aluminum alkoxide condensation catalyst is passed to saidreaction zone.

6. A process according to claim 1 wherein the overhead distillatestreams from said second, fifth and seventh distillation zones are fedto an aluminum alkoxide condensation catalyst formation zone wherein aning zone is maintained at an elevated temperature of about 30 C.

8. A process according to claim 1 wherein said aluminum alkoxidecondensation catalyst is fed into said reaction zone at a rate of about0.1 to about 5.0 percent by weight of the total reactants.

CERTiFlQATE @F @QRREWHQN Patent No. 3,714,236 Dated nuarv q. 1973Inventor) Howard N. Wright, Jr. Hugh 3. Hagemeyer, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the abstract, line 5, the first Word should be --production-, I notprodu'ct".

Column 5, line 2, "24 hours" should be --24 hour--.

Column 7, line l3, delete "3.0 percent and 48.8. percent is butylacetate." and insert -3.0 percent isobutanoland 48.8 percent isobutylacetate.-

Column 7, line 61, after column 1', insert a period I Column 9, line1,5, delete Ol0 C" and insert 0-l0C.--.

Column 9, line 21, after "isobutyrate", insert a semicolon Column 10,line 23, delete "to and insert --at 7 Column 10, line 27, delete thesecond "isobutyl".

Signed and sealed this 10th day of July (SEAL) Attest: v

EDWARD M.FLETCHER,J R. Rene Tegtmeyer Attesting Officer ActingCommissioner of Patents TEC 10261

1. A continuous process for the preparation and recovery of essentiallypure esters from acetaldehyde and isobutyraldehyde essentially free ofethyl isobutyrate contaminant which comprises:
 1. introducing into areaction zone essentially dry, acid-free reactants comprising a mixtureof acetaldehyde and isobutyraldehyde, condensing said reactants at acondensation temperature of about 0*-10* C in the presence of analuminum alkoxide condensation catalyst for about 3 to 6 hours toconvert at least 90 percent of said reactants to a reaction productmixture comprising ethyl acetate, isobutyl acetate, isobutylisobutyrate, and ethyl isobutyrate
 2. passing said reaction productmixture and unconverted reactants to a holding zone maintained at atemperature of between about 20* C. to about 40* C. for about 5 to 30hours to substantially complete condensation of said unconvertedreactants;
 2. A process according to claim 1 wherein the overheaddistillate stream from said seventh distillation zone is fed to analuminum alkoxide condensation catalyst formation zone wherein analkanol, halogen and aluminum metal are introduced to form an aluminumalkoxide condensation catalyst, a solution of aluminum alkoxidecondensation catalyst is withdrawn from said condensation catalystformation zone and said solution of aluminum alkoxide condensationcatalyst is passed to said reaction zone.
 3. A process according toclaim 1 wherein the overhead distillate stream from said fifthdistillation zone is fed to an aluminum alkoxide condensation catalystformation zone wherein an alkanol, halogen and aluminum metal areintroduced to form an aluminum alkoxide condensation catalyst, asolution of aluminum alkoxide condensation catalyst is withdrawn fromsaid condensation catalyst formation zone and said solution of aluminumalkoxide condensation catalyst is passed to said reaction zone. 3.passing the resulting reaction product mixture of said holding zone to afirst distillation zone maintained at about atmospheric pressure with atop temperature of from about 78* C. to about 117* C., withdrawingtherefrom an overhead distillate stream comprising aldehydes, ethylisobutyrate, ethyl acetate, isobutyl acetate, isobutanol and low boilingimpurities and a bottom residual stream comprising isobutanol, isobutylisobutyrate, glycol esters and catalyst residue, passing said overheaddistillate stream to a second distillation zone maintained at from aboutatmospheric to about 100 psig pressure with a top temperature of fromabout 60* C. to about 78* C. at atmospheric pressure;
 4. withdrawingfrom said second distillation zone an overhead distillate streamcomprising aldehydes, ethyl acetate, and low boiling impurities and abottom residual stream comprising ethyl acetate, isobutyl acetate andhigh boiling impurities, passing said bottom residual stream to a thirddistillation zone maintained at about atmospheric pressure with a toptemperature of about 77* C.;
 4. A process according to claim 3 whereinsaid aluminum alkoxide condensation catalyst formation zone ismaintained at a temperature of between about 110* C. and about 130* C.5. A process according to claim 1 wherein the overhead distillate streamfrom said second distillation zone is fed to an aluminum alkoxidecondensation catalyst formation zone wherein an alkanol, halogen andaluminum metal are introduced to form an aluminum alkoxide condensationcatalyst, a solution of aluminum alkoxide condensation catalyst iswithdrawn from said condensation catalyst formation zone and saidsolution of aluminum alkoxide condensation catalyst is passed to saidreaction zone.
 5. withdrawing from said third distillation zone anoverhead distillate product stream consisting essentially of ethylacetate and a bottom residual stream comprising isobutyl acetate andhigh boiling impurities, passing said bottom residual stream to a fourthdistillation zone maintained at about atmospheric pressure with a toptemperature of from about 108* C to about 117* C.;
 6. withdrawing fromsaid fourth distillation zone an overhead distillate stream comprisingisobutyl acetate and low boiling impurities and a bottom residual streamcomprising isobutyl acetate and high boiling impurities, passing saidoverhead distillate stream to a fifth distillation zone maintained atabout atmospheric pressure with a top temperature of from about 108* C.to about 117* C. and returning said bottom residual stream to said firstdistillation zone;
 6. A process according to claim 1 wherein theoverhead distillate streams from said second, fifth and seventhdistillation zones are fed to an aluminum alkoxide condensation catalystformation zone wherein an alkanol, halogen and aluminum metal areintroduced to form an aluminum alkoxide condensation catalyst, asolution of aluminum alkoxide condensation catalyst is withdrawn fromsaid condensation catalyst formation zone and said solution of aluminumalkoxide cOndensation catalyst is passed to said reaction zone.
 7. Aprocess according to claim 1 wherein said holding zone is maintained atan elevated temperature of about 30* C.
 7. withdrawing from said fifthdistillation zone an overhead distillate stream comprising isobutylacetate and low boiling impurities, a side product stream consistingessentially of isobutyl acetate, and a bottom residual stream comprisingisobutyl acetate, acetals and high boiling impurities; returning saidbottom residual stream to said first distillation zone;
 9. withdrawingfrom said sixth distillation zone a bottom catalyst sludge streamcomprising glycol esters and catalyst residue and an overhead distillatestream comprising isobutyl isobutyrate and isobutanol, passing saidoverhead distillate stream to a seventh distillation zone maintained atfrom about 100 mm mercury to about atmospheric pressure with a toptemperature of about 108* C. to about 147* C. to atmospheric pressure;and
 10. withdrawing from said seventh distillation zone an overheaddistillate stream comprising isobutanol and low boiling impurities and aside product stream consisting essentially of isobutyl isobutylisobutyrate.